This description relates to methods and apparatus for dissipating heat from electrical components located within a housing.
In amplifiers and other electrical devices, various electrical components contained within the device housing generate heat while operating and require cooling for proper operation. In one example, the electrical components are integrated circuits mounted to a circuit board which are cooled by dissipating heat generated to the ambient surroundings. Improved heat transfer and cooling of the electrical components is accomplished by positioning the electrical components proximate to a heat sink. Heat sinks are generally large metallic structures made from a highly heat conductive material, such as aluminum, for example, and include an expansive surface area formed by a number of fins for improved convective heat transfer to the ambient surrounding. The heat sink itself can form the chassis for the electrical device, housing a circuit board populated with electrical components, for example. In particular, amplifiers designed for vehicle audio systems have unique cooling requirements given the typical physical limitations for mounting the amplifier in the vehicle and the relatively high power levels and number of audio channels.
As shown in FIG. 1, an amplifier 20 includes a heat sink 25 which forms a chassis for supporting the electrical components of the amplifier. The heat sink has cooling fins 30 which extend from at least one surface of the heat sink and a substantially planar housing cover 35. As shown in FIG. 2, with the cover removed from the heat sink, a circuit board 40 includes one or more electrical components. Referring to FIGS. 3A and 3B, the circuit board supports electrical components 45a, 45b, 45c and 45d (collectively 45), which may be integrated circuits, for example. The reverse side of the circuit board is shown in FIG. 3B, with the corresponding locations of the electrical components 45 shown in phantom. The circuit board is disposed in the heat sink such that the electrical components are in substantial contact with component pads 50a, 50b (FIG. 5) of the heat sink 25. The component pads extend from the heat sink toward the electrical components to provide a conductive thermal pathway for heat dissipation to the ambient surroundings.
Referring to FIG. 4, housing cover 35 is secured to the heat sink with fasteners extending through screw holes 55 and includes projections 60a, 60b, 60c and 60d (collectively, 60) and can include a number of ventilation holes 70. The location of the projections correspond to the location of the electrical components 45 on the circuit board, such that when the housing cover is fastened to the heat sink, the projections 60 engage the electrical components between the component pads 50 and the circuit board. In so doing, resistance to heat transfer from the components to the heat sink is reduced, and the heat generated in the electrical components is more effectively transferred to the heat sink.
With reference to FIG. 5, two adjacent component pads 50a, 50b can have different heights, as can the associated projections 60a, 60b and/or the electrical components 45a, 45b, when accounting for stack-up tolerances. When the electrical components 45a, 45b are adjacent to one another, the associated projections are located adjacent one another. Given the close proximity of projection 60a to 60b (and similarly, 60c to 60d), vertical movement of projection 60a is strongly coupled to the movement of projection 60b. Accordingly, if projection 60a presses the electrical component 45a against component pad 50a, projection 60b will be limited by projection 60a, as both proximally extend from the same substantially rigid cover. The disparities in height noted above can lead to a gap 63 between electrical component 45b and projection 60b that interrupt or diminish proper cooling of the electrical components.
Attempts to reduce or bridge this gap and improve the cooling of the electrical components are described in U.S. Pat. No. 7,082,034. In this regard, U.S. Pat. No. 7,082,034 describes a housing cover to cause electrical components to engage with at least one component pad of a heat sink. The housing cover includes one or more projections which are integrally formed from the housing cover and positioned for biasing the electrical components against the component pad. The housing cover also includes a mechanism that permits a vertical displacement of the projection relative to the vertical displacement of the housing cover. Slots extend around at least part of the projection so as to substantially decouple vertical displacement of the projections from a vertical displacement of the housing cover. In some cases, a linkage is attached to adjacent ones of the projections such that an upward deflection of a first one the projections results in a downward deflection of the other, adjacent projection. While such configurations can be effective to reduce gaps between the electrical components and the heat sink, the incorporation of slots into the housing cover can allow moisture and debris into the region of the circuit board.
Other attempts to reduce or bridge this gap and improve the cooling of the electrical components include the use of intermediate elements between the electrical component and the component pads such as clips, springs, gels, putty, or foam, for example. Such measures add additional components and cost to the manufacturing and assembly process and may not always maintain sufficient contact between the electrical component and the component pad, which may lead to overheating and failure of the electrical components.